1. Field of the Invention
The present invention relates to a capacitor power supply having a capacitor unit that is a plurality of capacitors connected in series, a power monitoring device for use therewith, a method of monitoring power, and a method of manufacturing the capacitor power supply.
2. Description of Related Art
Electrochemical capacitors that use an electric double-layer (hereinafter, “capacitors”) have a longer life cycle and are more capable of rapid charging and large current discharge than conventional secondary batteries. Therefore, there is hope for these capacitors to be a storage device that can be used for energy regeneration and the like.
When using capacitors to regenerate energy, reclaim energy, and the like, for example, it is common to form a capacitor module in which a plurality of capacitors are connected in series, due to the low rated voltage of the capacitors.
When charging and discharging these capacitors that are connected in series, however, variation occurs in the voltages between the terminals of the capacitor modules due to differences in the electrostatic capacitances of the individual capacitors and because of leakage current. In such a case, one capacitor among the plurality of capacitors exceeding the rated voltage will cause degradation of this single capacitor. If the voltage applied to the individual capacitors is set to be low so as to not exceed the rated voltage, then the capacitances of the capacitors cannot be used effectively.
An unequal voltage suppression circuit disclosed in Patent Document 1 includes switches and resistors connected to respective capacitors in parallel. When capacitors are being charged, this circuit monitors the voltage between the terminals of the respective capacitors and closes a switch connected to one or more capacitors that have a voltage between the terminals thereof higher than a prescribed tolerance level, which is higher than the voltage between the terminals of the other switches, for example. Thereafter, the current is consumed by the resistor connected to these capacitors, and the amount of charge to these capacitors is reduced. Therefore, the rate of increase of voltage between the terminals of these capacitors is slower than the rate of increase of voltage between the terminals of other capacitors that do not have a resistor connected thereto. As a result, variation in voltage between the respective terminals is suppressed during charging (see paragraph [0022] in the specification of Patent Document 1, for example).
A cell monitoring unit in a cell monitoring device disclosed in Patent Document 2 includes a balancer having resistors and switches respectively connected in parallel to a plurality of battery cells that are connected in series. When a switch of the balancer is ON and OFF, the cell monitoring unit measures the voltage of the battery cells by using a voltage measuring circuit, and if the difference in the measured voltage during ON and OFF is larger than a threshold, an abnormality of the battery cells or circuits is judged to have occurred (see paragraph [0018] in the specification of Patent Document 2, for example).